In addition to the usual and familiar functions of providing for ingress and egress into/from the cabin of an aircraft, aircraft doors must typically perform other functions. For one, they must contribute to the structural integrity of the aircraft. For another, aircraft doors should be designed so as to not interfere with the aircraft's flight performance. Further, in the specific case of a pressurized aircraft, an aircraft door must also be engineered to become an integral part of the pressure vessel when the aircraft is pressurized. The importance of this last point is underscored by a simple example. For a fifteen square foot door area, a pressure differential of ten pounds per square inch (Δp=10 psi), between the inside and the outside of the aircraft at altitude, will exert a total force against the inside of the door equal to 21,600 lbs. The door and fuselage, of course, must react to this force. Clearly, aircraft door design is a major consideration.
In general, when high pressure differentials are required (e.g. Δp>5 psi), the design of doors for pressurized aircraft have typically required that the door somehow overlap and grip the door frame on the fuselage. Importantly, this is most effectively accomplished with an overlap from inside the aircraft. With such designs, the pressure differential at altitude will effectively “push” the door against the door frame. A consequence of this has been that the door itself is necessarily larger than the doorway opening. Accordingly, with such a design, ingress and egress to the cabin is only possible if the door can somehow be retracted into the cabin. For large aircraft, this has been acceptable. For smaller aircraft, however, this solution may well be unacceptable or, at best, inconvenient.
In light of the above, it is an object of the present invention to provide an assembly suitable for the purposes of providing a door for a pressurized plane which opens and extends outwardly from the aircraft fuselage when the plane is depressurized. It is another object of the present invention to provide assemblies and methods to create a pressure seal with door overlap from inside the aircraft during aircraft pressurization, while providing for an external extension of the door from the aircraft when the aircraft is depressurized. It is yet another object of the present invention to provide assemblies and methods for operating a cabin door of a pressurized aircraft which allows portions of the door to engage with the aircraft fuselage from inside the cabin for a closed configuration, yet be positioned outside the aircraft when the door is in an opened configuration. Still another object of the present invention is to provide a door assembly for a pressurized aircraft that can be opened and closed easily and that is extremely reliable.